đâu?

1. have

2. invite

3. nervous

4. free

5. worry

6. fifth

7. nineteenth

8. twelveth

Hmu hmu 9h mik fải tắt máy r 

ok bn

455,64

46.A

47.C

48.A

49.C

50.B

\(M=\dfrac{2}{1\times2}+\dfrac{2}{2\times3}+...+\dfrac{2}{50\times51}\)

\(M=2\times\left(\dfrac{1}{1\times2}+\dfrac{1}{2\times3}+...+\dfrac{1}{50\times51}\right)\)

\(M=2\times\left(\dfrac{2-1}{1\times2}+\dfrac{3-2}{2\times3}+...+\dfrac{51-50}{50\times51}\right)\)

\(M=2\times\left(\dfrac{2}{1\times2}-\dfrac{1}{1\times2}+\dfrac{3}{2\times3}-\dfrac{2}{2\times3}+...+\dfrac{51}{50\times51}-\dfrac{50}{50\times51}\right)\)

\(M=2\times\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{50}-\dfrac{1}{51}\right)\)

\(M=2\times\dfrac{50}{51}\)

\(M=\dfrac{100}{51}\)

17. C

18. A

19.C

20. C

21. B

22.B

1.B

2.C

3.A